1. Field of the Invention
The present invention relates to data-link processing equipment connected to a plurality of digital transmission lines and an apparatus for a subscriber terminal office using this processing equipment.
In the apparatus for a subscriber terminal office, it is necessary to expand the scale of the equipment or to install a large capacity equipment in accordance with the demands to increase the number of the subscribers which is to be accommodated. The amount of processing of the data link for transmitting and receiving the control data is also increased along with this. Accordingly, it has become necessary to make the data-link processing more efficient.
2. Description of the Related Art
As will be explained later in detail with reference to the drawings, in the apparatus for a subscriber terminal office of ordinary subscribers, for example, 96 subscribers are regarded as one control unit. At the level of DS1 signal, four transmission lines or two transmission lines are allocated for each above control unit. In this case, the number of the subscribers accommodated in a conventional apparatus for a subscriber terminal office is on the order of 96 or 192. Accordingly, the number of the data links becomes four or two, and it is possible to individually process the data links.
However, if the capacity of the apparatus for the subscriber terminal office is made larger and the number of the accommodated subscribers is increased a few times to 10 times the number of the subscribers mentioned before, the data links to be processed would be greatly increased. Accordingly, if the processing of the data links is achieved individually, it would lead to an enlargement of the scale of the apparatus and thereby a configuration of the apparatus would result in a low efficiency.
Therefore, a configuration for commonly processing a large number of data links can be considered by a person skilled in the art. In this case, consideration may be given to a configuration in which phase adjustment is performed so that the same frame synchronization timing is established with respect to the transmission lines and then the data link data is demultiplexed to process the data-link data by a commonly provided processor. However, the delay times of the transmission lines differ, and so the timing of the frame synchronization at each transmission line is different. For this reason, when matching the timings of the frame synchronizations, there may exist a transmission line which requires very long phase adjustment time. In such a case, the transmission lines must be aligned to the transmission line having the longest delay time, so there arises a problem of an increase of the processing delay of the data-link data.